The present invention is generally directed to processes for the preparation of particles, and more specifically to processes for the preparation of toner compositions. In one embodiment, the present invention relates to the economical preparation of particles, especially toner compositions with an average particle diameter of less than 20 microns, and preferably from about at least 3 to about 12 microns by the melt mixing, or coextrusion of at least two polymer components. Another embodiment of the present invention is directed to a simple economical one step process for the preparation of particles including dry and liquid toner compositions by the formation of rubbery, glassy, or semicrystalline domains in an incompatible continuous phase of a water soluble polymer by melt mixing, dissolving the aforesaid continuous phase with, for example, water or other suitable solvent, and recovering the resulting desired particles by, for example, filtration. Also, the present invention is directed to simple economical process for the preparation of toner particles from rubbery elastic nonjettable polymers in a manner, for example, wherein incompatible polymers are melt extruded or melt mixed such that one of the polymers becomes melt dispersed and segregated into toner sized domains in a continuous phase of water soluble plastic. When the continuous phase is dissolved with, for example, an alcohol or water, discrete ellipsoidal and/or spheroidal toner size particles remain of an average diameter of from about 3 to about 20 microns. Moreover, in a specific embodiment of the present invention there is provided a process for the preparation of particles, including toner particles, which comprises adding to an extruder or, for example, a BANBURY mixer two mutually insoluble polymers, one of which is soluble in a solvent such as an alcohol or water, and one of which is not soluble in the solvent, melt extruding or melt mixing the two polymers, thereby resulting in an incompatible continuous phase of the solvent soluble polymer, dissolution of the solvent soluble polymer in the solvent, and recovery of the insoluble polymeric product particles. The particles resulting from the process of the present invention can be selected as toner compositions when admixed with pigment particles, and are useful in xeromammography, especially those toner particles with an average diameter of about 8 microns, and the like. Also, the particles obtained with the process of the present invention can be selected for liquid ink development processes wherein small particles, for example with an average diameter of from about 3 to about 20 microns, can be selected to develop images; as ultra-low energy fusing, that is for example from about 50.degree. to about 150.degree. C., toners obtained from polymers with low glass transition temperatures; as small, for example with an average diameter of from about 3 to about 15 microns, particle pigment-polymer dispersions suitable for thermal ink jet systems; for obtaining toner particles for polymers too tough (for example, polyvinyl butyral) or with substantial rubbery characteristics; and medical diagnosis, affinity chromatography, membranes, cosmetics, prostheses, and the like. With the processes of the present invention for the preparation of toner particles, there is avoided the need for a jettable polymer. Jettable polymers include those with, for example, a glass transition temperature above the processing temperature, usually about 25.degree. C. There is also provided in accordance with the present invention processes with positively or negatively charged toner compositions comprised of resin particles, pigment particles, optional additives including waxes, especially those with hydroxyl functionality, carboxyl functionality and charge enhancing additives. In addition, the present invention is directed to developer compositions comprised of the aforementioned toners, and carrier particles. Further, the processes of the present invention with the toner and developer compositions illustrated, including single component toners, enable reliable output copy quality and stable triboelectric charging properties for the toner compositions selected. Also, with the processes of the present invention low glass transition temperature polymers, semicrystalline polymers, and liquid polymers can be processed into small particles of from about 3 to about 15 microns.
Developer and toner compositions with certain waxes, and the preparation thereof are known. For example, there are disclosed in U.K. Patent Publication 1,442,835, the disclosure of which is totally incorporated herein by reference, toner compositions containing resin particles, and polyalkylene compounds, such as polyethylene and polypropylene of a molecular weight of from about 1,500 to 6,000, reference page 3, lines 97 to 119, which compositions prevent toner offsetting in electrostatic imaging processes and can be prepared by melt mixing processes. Additionally, the '835 publication discloses the addition of paraffin waxes together with, or without a metal salt of a fatty acid, reference page 2, lines 55 to 58. In addition, many patents disclose the use of metal salts of fatty acids for incorporation into toner compositions, such as U.S. Pat. No. 3,655,374. Also, it is known that the aforementioned toner compositions with metal salts of fatty acids can be selected for electrostatic imaging methods wherein blade cleaning of the photoreceptor is accomplished, reference Palmeriti et al. U.S. Pat. No. 3,635,704, the disclosure of which is totally incorporated herein by reference. Additionally, there are illustrated in U.S. Pat. No. 3,983,045 three component developer compositions comprising toner particles, a friction reducing material, and a finely divided nonsmearable abrasive material, reference column 4, beginning at line 31. Examples of friction reducing materials include saturated or unsaturated, substituted or unsubstituted, fatty acids, preferably of from 8 to 35 carbon atoms, or metal salts of such fatty acids; fatty alcohols corresponding to said acids; mono and polyhydric alcohol esters of said acids and corresponding amides; polyethylene glycols and methoxy-polyethylene glycols; terephthalic acids; and the like, reference column 7, lines 13 to 43.
Toner compositions can be prepared by rubber roll milling, (extrusion) melt blending, air jetting, spray drying, cryogenic attrition, melt dispersion, cold melting and attrition of swollen gels, controlled crystallization, melt congealing, encapsulation, in situ polymerization, sonification, filament grinding, heat spheroidization and the like. In extrusion process, there is generally added to an extrusion device polymer particles and pigment particles. There results strands of toner particles that are severed, and thereafter the particles are jetted and classified. With the process of the present invention, there are obtained toner size particles without jetting and if desired without classification thus avoiding further processing costs. Also, with the aforementioned melt mixing or extrusion processes there cannot usually be selected rubbery polymers with low glass transition temperatures, semicrystalline polymers, or tough polymers which do not fracture readily.
As a result of a patentability search, there were located U.S. Pat. Nos. 4,222,982 and 4,233,388 which illustrate the formation of toners by melt extrusion; U.S. Pat. No. 2,470,001 which discloses the use of an extruder as a mechanism for blending and working two ingredients; and Canadian Patent 1,183,033 which relates to the preparation of toners wherein, for example, two incompatible resins are melt blended, and wherein one resin forms a discontinuous phase with the other.
Other patents of interest which disclose toner compositions and the preparation thereof include U.S. Pat. Nos. 4,072,521; 4,073,649 and 4,076,641. Furthermore, references of background interest are U.S. Pat. Nos. 3,165,420; 3,236,776; 4,145,300; 4,271,249; 4,556,624; 4,557,991 and 4,604,338.
In U.S. Pat. No. 4,883,736 the disclosure of which is totally incorporated herein by reference, there are illustrated toner compositions, including magnetic single component, and colored toner compositions containing certain polymeric alcohol waxes, which toners can be prepared by known methods, including melt mixing by extruding, spray drying, and the like. More specifically, there is disclosed in the '736 Patent the elimination of toner spots or comets with developer compositions comprised of toner compositions containing resin particles, particularly styrene butadiene resins, pigment particles such as magnetites, carbon blacks or mixtures thereof, polymeric hydroxy waxes available from Petrolite, which waxes can be incorporated into the toner compositions as internal additives or may be present as external components, it being noted that with the processes of the present invention these additives are usually present as internal components; and optional charge enhancing additives, particularly, for example, distearyl dimethyl ammonium methyl sulfate, reference U.S. Pat. No. 4,560,635, the disclosure of which is totally incorporated herein by reference, Hodogaya Chemical TP-302 and Orient Chemical BONTRON P-51, and the like; and carrier particles. As preferred carrier components for the aforementioned compositions, there are selected steel or ferrite materials, particularly with a polymeric coating thereover, including the coatings as illustrated in U.S. Ser. No. 751,922, (now abandoned) entitled Developer Composition with Specific Carrier Particles, the disclosure of which is totally incorporated herein by reference. One particularly preferred coating illustrated in the aforementioned application is comprised of a copolymer of vinyl chloride and trifluorochloroethylene with conductive substances dispersed in the polymeric coating inclusive of, for example, carbon black. In one embodiment, disclosed in the aforementioned application is a developer composition comprised of styrene butadiene copolymer resin particles, and charge enhancing additives selected from the group consisting of alkyl pyridinium halides, ammonium sulfates, and organic sulfate or sulfonate compositions; and carrier particles comprised of a core with a coating of vinyl copolymers, or vinyl homopolymers. The polymeric components of the aforesaid application are also selected for various embodiments of the present invention as illustrated herein.
The preparation of toner and developer compositions containing charge enhancing additives, especially additives which impart a positive charge to the toner resin, are well known as indicated herein. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of certain quaternary ammonium salts as charge control agents for electrostatic toner compositions. There are also described in U.S. Pat. No. 2,986,521 reversal developer compositions comprised of toner resin particles coated with finely divided colloidal silica. Further, there is illustrated in U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, developer and toner compositions having incorporated therein as charge enhancing additives organic sulfate and sulfonate compositions; and in U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, positively charged toner compositions containing resin particles and pigment particles, and as a charge enhancing additive alkyl pyridinium compounds, inclusive of cetyl pyridinium chloride. The aforementioned toners are prepared generally by melt mixing processes, rubber roll milling and extrusion.
Other prior art disclosing positively charged toner compositions and processes thereof, including melt mixing with charge enhancing additives, include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014 and 4,394,430.
Although the above described processes for the preparation of toner and developer compositions are useful for their intended purposes, there is a need for improved processes. More specifically, there is a need for processes wherein particles, especially toner particles, are obtained by a melt mixing process wherein jetting is avoided. Rather, with the process of the present invention there results toner size particles formed during melt mixing or extrusion. Also, there is a need for processes wherein rubbery elastic nonjettable polymers may be selected. Additionally there is a need for small, from about 3 to about 15 microns average diameter, toner particles of consistent size and shape suitable for mammography, liquid ink development, and high-resolution xerography, especially color xerography. Also, there is a need to process toners obtained from tough nonjettable materials (such as polyvinylbutyral) thereby, for example, increasing developer life as compared to several prior art toners.